Induction of long-lived plasma cells producing protective HIV Envelope (Env)-specific antibody that is distributed systemically and at mucosal sites is a primary objective of current HIV vaccine strategies. However, little is known about the development, localization, and maintenance of human plasma cells in response to HIV vaccination strategies. It is generally understood that following vaccination in humans, long-lived plasma cell precursors develop in the draining lymph nodes, are transiently present systemically (observed as related peripheral blood plasmablasts), and then migrate to the bone marrow, where they persist for months to years as long-lived plasma cells and are the predominant source of serum antibody. Substantial variations in the persistence of the resulting antigen-specific serum Ab following vaccination or infection have been observed, and may be related to the form of the antigen, the context of the initial primary response (e.g. T cell help), or inheren to the responding B cell. We hypothesize that variations in priming strategies will result in differences in the origin, phenotype, immunoglobulin (Ig) repertoire usage, and composition of the human HIV-specific plasma cells. Using samples obtained from participants in the HVTN105 Phase I Trial, which is testing various DNA and protein (AIDSVAX B/E) immunogen priming combinations, we propose to address this hypothesis. Due to the extensive mutation often observed in HIV broadly neutralizing Abs, their often poor recognition of HIV Env when reverted to germline, and their frequent association with self-reactivity that we and others have described, it remains unclear if such protective B cells arise from the initial engagement of a naive B cell with HIV Env, or are the consequence of pre-existing non-HIV antigen-experienced memory B cells engaging HIV Env through cross-reactivity. The properties of that initial cell type, whether naive or a pre-existing memory subset, are likely to profoundly influence its immunoglobulin repertoire usage and the ability to develop a desired long-lived protective serum Ab response. Through longitudinal deep Ig sequencing we propose to track back the HIV-specific Ig sequences from the peripheral blood plasmablast population to baseline samples to determine the origin of the Env-specific plasmablasts. The presence of protective HIV Env-specific Ab at mucosal sites is a desired goal of HIV vaccine strategies; however, the cellular source of these antibodies is poorly defined. The specific repertoire relationships between plasma cells of different locations remains unclear, and warrants detailed analysis to determine to what extent measurement of serum Ab, as well as evaluation of blood plasmablasts and bone marrow plasma cells, can serve as a surrogate for the critical mucosal humoral response. Through longitudinal deep Ig sequencing, we propose to track the HIV-specific peripheral blood plasmablast population into the bone marrow, tonsil, and intestinal mucosa. Through the critical dissection of the human plasma cell response to HIV vaccination critical mechanisms determining breadth, durability and mucosal availability of protective antibody will be identified, to inform future rational vaccine development.